With continuous development of the science and technologies, the electromagnetic wave technologies have found wide application in various aspects of people's life gradually. An important property of electromagnetic waves is that they can propagate in any media or even in a vacuum. During propagation of an electromagnetic wave from a transmitting terminal to a receiving terminal, the energy loss has a direct impact on the propagation distance of the electromagnetic wave and on the signal transmission quality.
The electromagnetic wave suffers substantially no energy loss when propagating through a same medium. However, when the electromagnetic wave propagates through an interface between different media, partial reflection of the electromagnetic wave will occur. Usually, the larger the difference in electromagnetic parameter (e.g., dielectric permittivity or magnetic permeability) between the different media at two sides of the interface is, the more the reflection will be. Due to the partial reflection of the electromagnetic wave, the electromagnetic wave will suffer an electromagnetic energy loss in the propagation direction, which has a serious impact on the propagation distance of the electromagnetic wave and on the signal transmission quality.
Accordingly, researches have been made on impedance matching in order to reduce signal reflection when the electromagnetic wave propagates through an interface between different media. However, currently the researches on impedance matching during the electromagnetic wave transmission are still limited to be within circuits, and there is still no sophisticated technology directed to impedance matching during propagation of the electromagnetic wave in space.
Further, a wave-absorbing material can absorb and attenuate energy of an incident electromagnetic wave, and through the dielectric loss of the material, convert the energy of the incident electromagnetic wave into thermal energy or other forms of energy. Therefore, the wave-absorbing material is expected to find wide application in electromagnetic pollution control, production of stealth materials and so on. However, in order to make the wave-absorbing material absorb an incident electromagnetic wave as much as possible, heightened requirements arc imposed on the impedance-matching property of the wave-absorbing material. By the term “impedance-matching property”, it means that an impedance of the wave-absorbing material shall be equal to the free-space's impedance as far as possible so that the energy of the incident electromagnetic wave is absorbed as much as possible. Meanwhile, the attenuating property is also important for the wave-absorbing material. By the term “attenuating property”, it means that the incident electromagnetic wave that is absorbed must be consumed as much as possible. Because of the heightened requirements on these two properties, it is very difficult to formulate a wave-absorbing composite material having superior wave-absorbing performances. Moreover, because the wave-absorbing composite material generally has a poor impedance matching property as being limited by the physical property of the material itself, a high reflectance is presented to electromagnetic waves incident from the free space that propagate through the wave-absorbing composite material.